ssh warning: "X11 connection requests different authenticationprotocol"

[Philip J. Hollenback]

For no reason that I can discern, ssh connections to my server started
behaving oddly yesterday.  This is using ssh 2.0.13 client and server,
both running on RH6.0 machines.

Here's a sample ssh session:

$ ssh foobar
user's password: xxxxxxx

Last login: xxx
$
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.
X11 connection requests different authentication protocol: 'MIT-MAGIC-COOKIE-1' vs. ''.


And this just continues ad infinitum.

The offending code is in sshchx11.c, function  ssh_channel_x11_filter():

  /* Check if authentication protocol matches. */
  if (proto_len != x->ct->x11_fake_proto_len ||
      memcmp(ucp + 12, x->ct->x11_fake_proto, proto_len) != 0)
    {
      if (proto_len > 100)
        proto_len = 100; /* Limit length of output. */
      ssh_warning("X11 connection requests different authentication
protocol: '%.*s' vs. ' %.*s'.",
                  x->ct->x11_fake_proto_len, x->ct->x11_fake_proto,
                  proto_len, (const char *)(ucp + 12));
      return SSH_FILTER_DISCONNECT;
    }


So why has this problem just started occuring?  I tried a debug version
of ssh, and it didn't give me any more useful information.  I should
note that the connection actually works fine - you can run X programs,
etc.  The X11 warning message just keeps printing on the screen, several
every second.

P.

-- 
Phil Hollenback
Veridicom, Inc.